The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Hyalography                                          Hydrobromic Acid
Hyalography, Photographic (vakos, glass or crystal). Nu-merous processes for photographic etching on glass come under this heading, many being due to Mr. Duchochois. The following is a simple method, giving good results. Paper is coated with the following: -
Water ... ...        ...        ...        ...      i oz.
Sugar... ... ...        ...        ...        ...    50 grs.
Gum arabic ... ...        ...        ...        ...    50 ,,
Ammonium bichromate      ...        ...        ...    50 ,,
Expose under a transparency and dust with fine bitumen, as in Powder Process (q.v.). Transfer to warm glass so as to soften bitumen, soak off paper, dry glass, and etch with vapour of Fluorhydric Acid (q.v.). (See Glass, Burnt in Photographs on, for a long list of books dealing with the various aspects of hyalography.)
Hydrates. Speaking strictly, the salts in which the group HO, or hydroxyl, acts as an acid group; thus, H.HO (water) is hydrogen hydrate, or it may be called hydroxyl mono-hydride. Popularly, a hydrate, or hydrated substance, is a compound of water with another substance. Thus, slacked lime may be regarded as calcic hydrate, Ca(HO).,, or as hydrated lime, CaO.H20.
Hydrazine. An alkali differing from ammonia by containing a smaller proportion of hydrogen, and which may be used in the developer. Formula N2H4.
Hydriodic Acid and Hydriodates (Ger., lodwasserstoff-sciure; Fr., Acide iodhydrique; Ital., Acido iodidricd). HI = i28. An acid which is easily decomposed with the liberation of iodine. It forms salts called iodides, or, when the base is non-metallic like aniline, the salt is called a hydriodate. In the case of ammonia both usages obtain.
Hydrobromic Acid (Ger., Bromwasserstoffsaure; Fr., Acide hydrobromique; Ital., Acido idrobromico). HBr=8i. An acid which is somewhat more stable than hydriodic acid, but less stable than hydrochloric acid; its salts (bromides or
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